Humidifying devices for humidifying air supplied to an enclosure or the like are known. The most notable of these prior art devices are misting devices that mechanically sling fine water droplets into a dry air stream with the idea that, if the droplets are small enough, they will quickly be absorbed and thus humidify the air.
One notable application for these humidifying devices is in aircraft environmental systems that provide humidified fresh air to crew members and passengers. The source of air for these systems is the air outside the aircraft which, at high altitudes, is extremely dry. After a few hours in this dry environment, crew members and passengers can become quite uncomfortable. This is especially true for crew members where high fresh-air flows are maintained to assure alertness. For these reasons, the fresh air delivered to crew members is often humidified on long flights.
The prior art humidifying devices have been found to be troublesome in several areas. The troublesome aspects of these devices create potentially adverse health and comfort conditions for persons exposed to the humidified air produced. In particular, bacteria can grow within these humidifying devices and can be readily dispelled with the humid fresh air. In addition, these devices allow liquid droplets to be delivered with the fresh air. Moreover, the potable water source for these devices usually contains minerals which eventually clog or foul equipment and, as a result, such minerals are dispelled with the air and leave deposits on exposed articles, such as electronic equipment. Accordingly, humidifying devices that correct these known deficiencies of the prior art devices have been sought.
Commonly assigned U.S. Pat. No. 5,348,691 to McElroy et al. discloses a membrane humidifying device that seeks to correct these deficiencies. The subject device comprises at least one membrane cell made up of at least one sheet of a hydrophilic membrane and at least one screen. The membrane cells are typically assembled when the membrane sheet(s) is wet and distended. In a preferred embodiment, two membranes are clamped in a frame and two screens, located between the membranes, are either clamped in the frame or loosely contained within the channel defined by the membranes.
Although such devices render acceptable humidification performance there is a need for membrane humidifying devices that provide increased humidification rates.
Moreover, it has been observed that during the cyclic operation of the devices of U.S. Pat. No. 5,348,691, the membranes of each cell expand during operation, and tend to move into the air passages, and then, during shut-down, contract as the membrane drys out. As a result, the cell hardware is stressed. Physical deformation of the cell frame supports and retainer sheets has resulted causing air leakage into the cell and non-uniform air flow between the cells. Accordingly, the humidification performance of these devices is less stable and therefore less predictable.
Thus, there is also a need for membrane humidifying devices that provide more stable and more predictable humidification performance.
It is therefore an object of the present invention to provide a method for improving and rendering more stable and predictable the humidification performance of membrane humidifying devices.
It is a more particular object to provide a method for improving water transport in membrane humidifying devices and for reducing membrane shrinkage stress on the cell hardware of such devices.
It is yet a more particular object to provide a method for treating the surfaces of membranes employed in the cells making up membrane humidifying devices so as to effect stable and increased humidification performance from such devices.
It is yet another object of the present invention to provide a membrane humidifying device made up of at least one cell employing membranes having such treated surfaces, and to provide a system employing such a device.